Basically the title. As much as possible male protagonist.
I just finished a reread of Suddenly Rich Kid. I seem to remember a similar story of a teen boy being suddenly sent to live with his dad, in Las Vegas. I think he lives in a guest house and his new sister introduces him to her friends. Not necessarily an elite school but definitely a high class student body.
Could someone help me identify the story.
Could be G Younger's The Valley that was pulled so it could be listed for sale somewhere. Link is to the Bookapy version.
The stories in https://storiesonline.net/series/1279/regan-riley-and-andy-drayton sort of fit (the second one more than the first one) because you did not specify that the MC has to attend the "elite high class school" himself.
In this story, his girlfriend does. The MC himself graduates from a spectacularly bad Highschool and part of the plot is the difference in the educational standards between the two schools.